Microstrip and micropatch microwave antenna elements are known in the art. They generally consist of a conductive or semiconductive material applied to a dielectric substrate by known techniques, such as sputtering, vapour deposition, and masking techniques. An element is active if, through an active circuit, for example an MMIC, it amplifies a received or transmitted signal.
The integration of antennas and active circuits is of great interest for: quasi-optical, spatial power combining, phased arrays; spatial frequency and polarization sensitive surfaces; and direct receiving arrays for microwave and sub-millimeter waves. In addition, there is great interest in using planar active arrays for microwave/millimeter wave imaging systems and radiometers in applications such as remote sensing, environmental studies, radio cameras, and radio astronomy.
For many practical applications, a number of discrete elements, up to several thousand, are applied to a substrate to form a phased antenna array. Generally, prior art phased arrays require complex feed networks for RF or IF signals. These networks can be highly lossy, bulky and expensive to design and produce.
Such feed networks are generally provided by microstrip transmission lines interconnecting the elements to a common feed. The networks are generally symmetrical patterns of transmission lines designed to feed signals in phase to or from the antenna elements. Therefore, beyond the complexity and attendant expense of providing such RF and IF feed networks, the failure of single transmission line or element can lead to catastrophic failure of the array by cutting the received or transmitted power from the array by up to half. For this reason, power combining in space using quasi-optical techniques with no feed network has emerged as an attractive alternative. This is especially useful at millimeter and sub-millimeter wavelengths where the feed networks are typically complicated, bulky, and lossy.
Various radiating array architectures have been proposed for output power combination. R. M. Weikle II et al., "Planar MESFET grid oscillator using gate feedback," IEEE Trans. Microwave Theory Tech., vol. MTT-40, pp. 1997-2003, 1992, and J. Birkeland et al., "A 16 element quasi-optical FET oscillator power combining array with external injection locking," IEEE Trans. Microwave Theory Tech., vol MTT-40, pp. 475-481, 1992 describe the use of number of sets of solid state oscillators as a power combining array. J. B. Hacker et al., "A 100 element planar Schottky diode grid mixer," IEEE Trans. Microwave Theory Tech., vol. MTT-40, pp. 557-562, 1992, discloses mixers forming a power combining array. J. A. Benet et al., "Spatial power combining for millimeter wave solid state amplifiers," 1993 IEEE MTT-S Int. Microwave Symp. Digest, Atlanta, pp. 619-622, and M. Kim et al., "A 100-element HBT grid amplifier" 1993 IEEE MTT-S Int. Symp. Digest, Atlanta, pp. 615-618, 1993 describes sets of amplifiers, each set integrated only with its own planar patch, radiating into space. The structures described in Benet et al. and Kim et al., respectively, are related to reflecting and transmitting amplifier surfaces. However, they are limited to the reflection and transmission of linearly polarized waves.
Active receiving, or transmitting, array architectures composed of active elements are also reported in the literature. Examples of such array architectures are described in W. Chew et al., "Printed circuit antennas with integrated FET detectors for millimeter-wave quasi optics", IEEE Trans. Microwave Theory Tech., vol. MTT-37, pp. 593-597, 1989; S. Weinreb, "Monolithic integrated circuit imaging radiometers," 1991 IEEE MTT-S Int Microwave Symp. Digest, Boston, pp. 405-408; K. Uehara et al., "Lens-coupled imaging arrays for the millimeter- and submillimeter-wave regions," IEEE Trans. Microwave Theory Tech., vol. MTT-40, pp. 806-811, 1992; and G. S. Dow et al., "W-band MMIC direct detection receiver for passive imaging system," 1993 IEEE MTT-S Int. Microwave Symp. Digest, Atlanta, pp. 163-166, 1993.
There are several drawbacks to the above designs. Generally, they tend to be expensive, and, therefore, unsuited to price sensitive commercial applications. It is necessary to custom design the elements and arrays for each application. And, in particular for oscillator power combining techniques, they are not suitable where amplification is required. Moreover, separate arrays are generally required for receiving and transmitting.